The organic EL (electroluminescent) device is being actively subjected to application study as a light emitting device of a high-speed response and a high light emission efficiency. The basic constitution thereof is shown in FIGS. 1A to 1C (see, for example, Macromol. Symp. 125, 1-48 (1997)).
As shown in FIGS. 1A to 1C, an organic EL device is generally composed of a transparent electrode 14 and a metal electrode 11 on a transparent substrate 15, and a plurality of organic film layers disposed between the electrodes.
In FIG. 1A, an organic layer consists of a light emitting layer 12 and a hole transport layer 13. As the material for the transparent electrode 14, a material with a large work function, such as ITO, is used to achieve good hole-injecting characteristics from the transparent electrode 14 to the hole transport layer 13. As the material for the metal electrode 11, a material with a small work function, such as aluminum, magnesium and alloys thereof, is used to achieve good electron-injecting characteristics to the organic layer. These electrodes generally have a thickness of 50-200 nm.
For the light emitting layer 12, an aluminoquinolinol complex (a representative example is Alq shown in FIG. 2) or the like is used. As the hole transport layer 13, for example, an electron-donating material such as a triphenylamine derivative (a representative example is α-NPD shown in FIG. 2) is used.
The organic EL device constructed as described above has a rectifying property, and when an electric field is applied so as to make the metal electrode 11 act as a cathode and the transparent electrode 14 act as an anode, electrons are injected from the metal electrode 11 into the light emitting layer 12, and holes are injected from the transparent electrode 14 into the light emitting layer 12.
When the injected holes and electrons recombine in the light emitting layer 12, excitons are formed to emit light. At this time, the hole transport layer 13 plays the role of an electron blocking layer to raise the recombination efficiency at the light emitting layer 12/hole transport layer 13 interface, and to enhance the light emission efficiency.
Furthermore, in FIG. 1B, an electron transport layer 16 is formed between the metal layer 11 and the light emitting layer 12 of FIG. 1A. Thus, the light emitting function can be isolated from the electron/hole transport function to make the carrier blocking action more effective, thereby improving the light emission efficiency. As the material for the electron transport layer 16, for example, an oxadiazole derivative or the like can be used.
Furthermore, as shown in FIG. 1C, an exciton-diffusion preventing layer 17 is additionally provided in order to confine excitons generated in the light emitting layer 12 within the light emitting layer 12 to effect efficient light emission.
Moreover, it is also possible to constitute an organic EL device with a single layer structure of an organic substance layer. Such a device is generally produced by forming a first electrode on a substrate, then forming a polymer film thereon by a coating method or the like, and forming a second electrode on the top thereof, but can also be produced by vacuum vapor deposition of low-molecular weight compounds.
Further, there are generally used two types of the light emitting layer, that is, a guest-host type wherein a light emitting material is dispersed in a carrier transport material, and another type wherein only a light emitting material is used in 100%. Most light emitting materials, when used in a high concentration in a light emitting layer, are liable to show a decreased light emission efficiency, and in such a case, it is preferable to select a suitable host material to adopt a guest-host type light emitting layer.
In the present invention, copper complex compounds of specific structures are employed as a light emitting material of an organic EL device.
As for the prior art concerning copper complexes, there are techniques using copper complex compounds different from the copper complex compounds employed in the present invention, but there are no disclosure of those copper complex compounds having sufficient performance to be used for display, illumination, or the like.
Examples of the prior art are identified as follows.    Document 1: Y. Ma et al., Advanced Materials, 1999, 11, No. 10, p85, High Luminescence Gold (1) and Copper (1) Complexes with Triplet Excited State for Use in Light-Emitting diodes    Document 2: Japanese Patent Application Laid-Open No. 10-308277 (Japanese Patent No. 2940514) to T. Azumaguchi et al.
There is a description therein that copper complexes can be produced at a relatively low cost and sufficiently drawing the performance of copper complexes makes it possible to provide low-cost, high-performance organic EL devices.
However, because EL devices obtained in the above documents have extremely low light emission efficiencies, and because there is no sufficient description in the above documents of the efficiencies of the devices, it is not believed that the characteristics of copper complexes were sufficiently drawn.